Definition:
The ratio of actual power being used in an alternating electrical circuit to the power which is apparently being drawn from the line. When the load in an a.c. circuit is purely resistive, such as is the case for ovens and incandescent lights, the actual and the apparent power are the same and the power factor is 100%. When the load includes elements such as a.c. motors, generators, transformers and other machinery with coils which introduce inductance, the sine wave of the current lags behind that of the voltage by an angle known as the phase angle, which is represented by the Greek symbol θ (theta). This angle ranges from zero (for a purely resistive load) to a theoretical maximum of 90° (for a purely inductive load). The cosine of this angle times 100 is the power factor, according to the formula: